Twitter revealed it found 2,752 accounts linked to the same Russian agency, many more than the 201 it initially reported in September.

There were also 1.4 million automated tweets about the election - around 0.74% of all election tweets.

Google said it had found $4,700 (£3,555) in Russia-linked ad spending during the time frame of the US election.

The information was disclosed by the internet giants to the Senate Judiciary Committee ahead of hearings on Tuesday and Wednesday.

Representatives of all three firms will face questions and detail Russia's impact on the popular sites when they appear before three congressional committees investigating Russian meddling in the 2016 US election.

Moscow has denied the claims, which Foreign Minister Sergei Lavrov dismisses as "fantasies".

3:33

Video:Trump aides under house arrest after denying charges linked to Russia probe

Twitter has suspended the accounts it found and passed on the details to congressional investigators.

In its written testimony, the company reportedly said: "State-sanctioned manipulation of elections by sophisticated foreign actors is a new challenge for us - and one that we are determined to meet."

The disclosures come as two former aides to Donald Trump are placed under house arrest following a sharp escalation in the FBI's investigation into Russian interference during the election.

The President's former campaign manager Paul Manafort and Mr Manafort's long-time business associate Rick Gates, have pleaded not guilty to charges including conspiring against the United States, money laundering and of being an unregistered agent of a foreign country.

In addition, George Papadopoulos, a former foreign policy adviser to Mr Trump's campaign, pleaded guilty to lying to the FBI about his Kremlin-related contacts.

The developments prompted a furious reaction from Mr Trump on Twitter: "Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign. But why aren't Crooked Hillary & the Dems the focus????? ....Also, there is NO COLLUSION!"

Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign. But why aren't Crooked Hillary & the Dems the focus?????